The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
Tympanic membrane perforation is one of the most common problems in otolaryngology. If left untreated, it is associated with significant morbidity such as hearing loss, recurrent otorrhea, middle ear infection and acquired cholesteatoma. Although most acute tympanic membrane perforations heal spontaneously, large or chronic tympanic membrane perforations, especially from chronic suppurative otitis media, often fail to heal and may require grafting.
In cases of chronic tympanic membrane perforation, a surgical procedure known as myringoplasty (or type I tympanoplasty) is required for closure of the perforation. Myringoplasty involves the use of a graft to “patch the perforation” and restore the integrity of the tympanic membrane; the purpose of which is to restore the continuity of the tympanic membrane to improve hearing and decrease the incidence of further middle ear infection.
Typically, an autograft (tissue obtained from the subject) is used with the most common type being temporalis fascia, which is considered the “gold standard” for tympanic membrane closure. Other types of commonly used autografts include cartilage, perichondrium and fat, and despite many studies comparing the efficacy of the various materials, there does not seem to be a clear consensus as to which is superior. Most purport success rates up to 90% regardless of the graft material or technique used. Despite this high success rate, reasons for graft failure may include instances of reperforation, cholesteatoma, lateralization, blunting, epithelial pearl and inclusion cysts.
Aside from this, there are other drawbacks associated with myringoplasty; it can be expensive, due to the requirement of anesthesia, surgery and an overnight hospital admission; has inherent morbidity and possible issues with defective donor sites. In addition, it has been recently argued that what is considered a success should be reviewed to include conditions of the middle ear, such as effusion, atelactasis and discharge, which could adversely affect the outcome. Transparency of the tympanic membrane has also been indicated as a factor that affects hearing with opaque membranes resulting in significantly higher hearing thresholds. Opacity was the result of thickening of the tympanic membrane; and increased thickness results in greater stiffness and diminished mobility. Similarly, autologous graft material tends to be opaque, thicker and more rigid than an undamaged tympanic membrane, adversely affecting acoustic transmission in addition to preventing the clinician from examining the middle ear for infection or defects during follow up.
The ongoing function of the repair may be influenced by the continued processes of retraction, cholesteatoma or reperforation and infection. Permanent conductive hearing loss can be caused by these continuing processes leading to erosion of the ossicles. The most common surgical approach then is to perform a tympanoplasty with a thicker layer of cartilage to resist further retraction and progression to retraction pocket formation, perforation and cholesteatoma. The cartilage can be used as an underlay, inlay or overlay graft.
However, as a result, these available methods using existing graft materials insufficiently replicate the microstructure and properties of native ear drums, hence premorbid hearing is not restored when they are used to repair perforated ear drums.
Moreover, the ear canal also plays a major role in modulating sound that is incident upon the tympanic membrane. The sharp anterior tympanomeatal angle, where the oblique ear canal meets the tympanic membrane, can significantly alter the sound pressure levels and impedances at various sites in front of the drum, especially at high frequencies. For this reason, the repair or reconstruction of the pars flaccida of the ear drum from degradation or other damage to the tissue and/or bone is often carried out in collaboration with tympanic membrane perforation repair, with the aim of restoring acoustic transmission and therefore premorbid hearing.
To date, a range of xenografts and synthetic materials, including Gelfoam®, and paper patch have been investigated as suitable scaffolds to support the regeneration of tympanic membranes. However, there is little evidence to support any of these as optimal materials for various types of perforations. Moreover, several commercially available xenografts such as porcine small intestine submucsa may evoke an inflammatory response due to the remnant xenocellular components using serotonin. In addition, synthetic materials are generally non-biodegradable, and their biomechanical and material properties are different compared to the normal tympanic membrane, which may affect the long-term hearing function. Hence there is a need for new materials for repairing ear drums and tympanic membrane perforations.